These are different aperture values f/1.4, f/2, f/2.8, f/4, f/5.6, f/8 (high to low)
It is calibrated in f/stops and is generally written as numbers such as 1.4, 2, 2.8, 4, 5.6, 8, 11 and 16. The lower f/stops give more exposure because they represent the larger apertures, while the higher f/stops give less exposure because they represent smaller apertures.

A lens that has an aperture of f/1.2 or f/1.4 as the maximum aperture is considered to be a fast lens, because it can pass through more light. This is the reason behind using lenses with large apertures that better suits low light photography.

Shutter speed also referred as exposure time is the time when the camera shutter is opened to expose sensor to the light. There are some times when you require fast speeds like sports or action photography, but there are other times that you can slow things down a little and get some very nice results indeed.

Shutter speed is generally measured in fractions of a second. Eg: 1/250 means one two-hundred-and-fiftieth of a second or four milliseconds. Most modern DSLRs cameras have shutter speeds of up to 1/4000th of a second, while some high end cameras can handle much higher speeds of 1/8000th of a second and even faster than that. The longest shutter speed on most DSLRs is typically 30 seconds i.e. without using external remote triggers.

Probably the most common settings for a DSLR used outside are 125th/sec at F8 or 250th/sec at F8.

The drive mode function within a camera can be used to change whether your camera shoots single or multiple shots once the shutter is full depressed. It can also be used to delay the shot by waiting 2 or 10 seconds to take a photo after the shutter has been pressed.